I recently had a nice conversation with Nathan Heffel for Colorado Matters at Colorado Public Radio. I revisited my data to confirm that Colorado is now the most polarized state legislature in the country, passing California in the past two years.

The plot below shows the trend over the past two to three decades, and it underlines the speed with which Colorado has polarized — the fastest in the country.

Breaking down the trend in polarization by party and chamber, it looks like the Republicans in both chambers and Democrats in the House have been largely responsible for this trend. Senate Democrats are fairly liberal but haven’t change much in the past few years.

The one update is that the posts here used the most recent publicly available version of our aggregate state legislative data. That data includes the years up through 2011. The Monkey Cage post uses a preliminary update to our data set, that brings the data to 2013.

We are working on polishing this data for public release shortly.

In the meantime, here are the new plots using that data set. The graph below shows legislative polarization in each state, averaging across all the years of our data (approximately 1996-2013) and across both legislative chambers. Polarization is defined as the average ideological distance between the median Democrat and Republican in the state legislature. Larger numbers indicate more division. The dashed line is the level of congressional polarization, included as a comparison (“US”).

About half of the states are even more polarized than Congress—which is saying a lot. At the same time, some states–like Louisiana, Delaware, and Rhode Island–have relatively less polarized state legislatures. In Louisiana, both parties are fairly conservative, and in Delaware and Rhode Island, they are both fairly liberal.

One state that stands out is California. It is incredibly polarized. (And its most recent primary and redistricting reforms look unlikely to reduce polarization.) Unlike Congress, however, Democrats both dominate the state so thoroughly and no longer need to attain supermajorities to pass budgets, so this polarization is not as much of an obstacle to actual lawmaking in the California state legislature.

Not only are states polarized, that polarization has increased over time. The graph below breaks down the trends in the ideology of Democrats and Republicans (measured by party medians) over time and across all 50 states. By convention, more positive scores represent more conservative preferences, and more negative scores represent liberal preferences. (One side-note: a data error exists in Washington State around the year 2000 and is being fixed.)

Most states have polarized over the past 20 years or so, but some more than others. Arizona, California, and Colorado are polarizing very fast. Nebraska—a state without formal political parties in its legislature—is polarizing very quickly too, though from a relatively low base.

Moreover, we are seeing asymmetric polarization, just as in Congress. Republicans have been getting more extreme faster than Democrats in more state legislative chambers, but this is by no means universally true across all states.

All in all, the picture we see in state legislatures is similar in many respects to Congress, but different in key points. The parties are pretty far apart on average, but that difference varies across the states. The parties are increasingly polarizing over time, but that too varies across state. Finally, we see cases of symmetric and asymmetric polarization. These new data on polarization at the state level—and the uneven pace of polarization across states—should help pundits and scholars figure out what’s driving polarization in our statehouses.

Over at American Legislatures, I show that, on the whole, polarization is asymmetric in the state legislatures. Republicans are polarizing faster across more states than Democrats. Examples include Tennessee and Colorado. But in lots of states, the patterns are different, where Democrats are leading the charge to extremism (eg, Idaho, Mississippi, and California). And both parties are polarizing roughly equally and simultaneously in places like Texas, Missouri, and Nebraska.

I just posted an updated visualization of state legislative polarization over at the Measuring American Legislatures blog.

Here’s a small version you can look at, but see the full post and explanation here. Look at California at the top with massive polarization, and Louisiana and Rhode Island at the bottom with relatively small amounts of partisan division.

My coauthor (Nolan McCarty) and I are releasing a new version of our state and chamber-level aggregate data. We have focused on two major updates:

In all, we have 140 chamber-years of new data. These now include party data for Nebraska thanks to friend andcoauthorSeth Masket, who generously provided the informal but well-known partisan affiliations for Unicameral legislators.

The individual level data underlying this release has been extensively cleaned to minimize the random noise inherent in acquiring roll call votes from printed journals.

Last Tuesday, Debra ‘Deb’ Fischer won a hotly contested Nebraska Republican primary election for the US Senate seat currently held by the retiring Ben Nelson. She beat Jon Bruning, the current Attorney General of the state, as well as third place challenger Treasurer Don Stenberg.

Most discussion on this election has focused on the surprising victory of Fischer, a rancher and sitting state senator (43rd district) who raised very little money, compared with the establishment front runner of Bruning. She was noted for being supported by former Alaska Governor and vice-presidential candidate Sarah Palin.

Much less well known is the ideological difference between the two candidates. It turns out that Bruning was a former state senator from the 3rd district, and thus I can estimate his ideological preferences from his roll call record (see details in my paper with Nolan McCarty here, and my blog posts on this data here.)

Did Sarah Palin get the pick right? Is Fischer the more conservative choice? The answer is yes. Fischer is in 96th percentile for conservatism in the officially nonpartisan Nebraska unicameral, and in the 93rd percentile of identified Republicans. That is, only 7 percent of Nebraska Republicans are more conservative than she in recent years. If her voting behavior was unchanged in the move from statehouse to Congress, she would be somewhere between Jim DeMint (R-SC) and Ron Johnson (R-WI) ideologically speaking. That’s pretty hard-core conservative.

Jon Bruning, on the other hand, is a moderate Nebraska conservative, located close to the middle of identified Republicans in the statehouse. That’s still fairly conservative, something close to deposed Bob Bennett of Utah or Elizabeth Dole of North Carolina.

Given how conservative of a state Nebraska is, I think Republican primary voters largely got this one right. Intrade’s market on this has Republican chances of success under Fischer at 69%, same as Nate Silver’s. I think that’s about right; Bob Kerrey is a pretty weak candidate for the Democrats. Fisher is no Scott Brown. There is no need to nominate a moderate to win the general election. Therefore, it is reasonable to nominate someone more extreme and still have a high likelihood of winning the election. Of course, while breaking out their champagne glasses, Nebraska conservatives must be hoping the statewide-untested Fischer isn’t another Sharron Angle…

That is, only 7 percent of Nebraska Republicans are more conservative than [Fischer] in recent years. . . . Jon Bruning, on the other hand, is a moderate Nebraska conservative, located close to the middle of identified Republicans in the statehouse. . . .

But then he concludes:

Given how conservative of a state Nebraska is, I think Republican primary voters largely got this one right.

How is it they “got this one right” if Fischer isn’t close to the median for Nebraska Republicans? Why wouldn’t it be getting it right to choose a candidate closer to their political views?

My response:

Of course, I was being a little bit glib. But here are my thoughts on this:

Yes, proximity is the yardstick, not directionality.

I was talking about Nebraska *conservatives*, not merely Republicans. NE conservatives surely live on the right hand side of the median Nebraska Republicans. In that case, Fischer at the 93rd percentile is more proximate to the 75th percentile Republican than Bruning at the 46th!

More broadly, of course, the calculation about whom to support is not only about proximity, but also about electability. So NE conservatives should weigh the potential benefits of a Fischer victory relative to Bruning by the probability that she wins relative to him.

What goes into that probability of victory? Proximity implies she’d be a WORSE candidate than Bruning, relative to the general election median.

On the other hand, partisanship dulls the effects of proximity. Jon Rogowski and I have a paper on this, showing that the proximity model works even in congressional elections, with the proviso that partisanship heavily moderates the effect. So, the dominance of Nebraska Republicans makes them somewhat insensitive to the difference between Fischer and Bruning. You can find the latest version of the paper here.

On the other hand, while Bruning has fought and won statewide office, Fischer hasn’t. Kerry has, but a long time ago. She might be a terrible candidate. It’s a gamble that I alluded to in the last line of the post to a fear that conservatives in the state might have — what if she’s another Sharron Angle?

So, what we have is a gamble. Fischer is probably less likely to win than Bruning against Kerry. But it appears that the payoff to winning is considerably higher for hard core conservatives in the state. If the drop in electability isn’t too bad (my guess, and that of preliminary evidence from the polls and markets), than she is the “right” choice for state conservatives.